In general, in the case of coloring a polymer molded article, dyes or pigments are used.
For example, in Patent Document 1, there is exemplified a color elution preventive method of a colored resin pattern in which in forming a colored resin pattern using a colored polyimide resin material having a dye incorporated into a polyamic acid, followed by a thermal treatment for curing, an aromatic diamine is previously added to the colored polyimide resin material, and the dye is coupled with a polyimidized polymer matrix via the aromatic diamine by a thermal treatment.
In patent document 2, there is disclosed a colored polyimide film for coating an electronic component containing a colored pigment in a resin component composed mainly of a polyimide resin obtained from an aromatic tetracarboxylic dianhydride, an aliphatic linear chain-containing aromatic diamine, and a siloxane diamine.
Pigments and dyes have both strong and weak points, respectively. For example, though the pigments are advantageous from the standpoint of heat resistance, they are difficult to be uniformly dispersed in a resin. Though the dyes have such an advantage that they are uniformly dispersed (or dissolved), they involve such a problem that they are easily eluted from a resin due to influences of a solvent or the like.
Incidentally, polyimide porous membranes are used for separators for batteries and diaphragms for electrolytic capacitors as well as for dust collection, precise filtration, separation, etc. and various production processes have been known.
For example, in Patent Document 3, there are disclosed a polyimide porous membrane having through-holes having a diameter of from about 0.01 to 10 μm and a process for production of a polyimide porous membrane comprising laminating a porous film on a cast film of a polyamic acid varnish and then dipping the laminate in a poor solvent.